Re: Signs are Not Constellations
Bunraku, on planet earth we have solstices and equinoxes. That's just the way it is. You understand the elementary science behind them.
Signs are 30-degree pie-sectors of the heavens, organized around the ecliptic.
If you do look at constellations and fixed stars, occasionally an out-of-bounds planet (or more commonly, asteroid) will nip into a constellation close to the zodiac, typically Cetus or Orion. (Ophichus passes through the ecliptic in a narrow part of the constellation.)
The standard constellations have been with us since ancient times. See, for example, Aratus, Phaenomena 3rd century BCE.